The present invention relates to an improved magnetic resistor sensor for an encoder, and more particularly relates to improvement in function of a magnetic resistor sensor which detects relative displacement of a magnetic recording medium by means of two magnetic resistor elements which change their respective inherent resistances in response to changes in the intensity of a magnetic field generated by the magnetic recording medium during the relative displacement.
In general, a rotary encoder includes a disc type magnetic recording medium and a magnetic resistor sensor arranged facing the magnetic recording medium for relative displacement therebetween.
A magnetic sine wave pattern having a wave length .lambda. is formed along the periphery of the magnetic recording medium. The magnetic resistor sensor includes a glass substrate and two magnetic resistor elements formed on the glass substrate via vacuum evaporation. Each magnetic resistor element is made of a material which, when placed in a magnetic field, changes its inherent resistance in response to change in intensity of the magnetic field. During the relative displacement between the magnetic recording medium and the magnetic resistor sensor, the magnetized pattern on the magnetic recording medium is detected by the magnetic resistor sensor to thus detect the magnitude and direction of the relative displacement.
The two magnetic resistor elements are arranged side by side in the direction of the relative displacement. One magnetic resistor element is adapted for detection of a sine wave component of the magnetized pattern and the other for detection of a cosine wave component of the magnetized pattern. The sine wave detecting magnetic resistor element includes a number of detecting sections arranged side by side in the direction of the relative displacement and adjacent detecting sections are joined by a connecting section. The cosine wave detecting magnetic resistor element has a substantially identical construction. The phases of the output signals issued by the sine wave and cosine wave detecting magnetic resistor elements lag one another by .lambda./4.
The distance between the longitudinal centers of the sine wave and cosine wave detecting magnetic resistor elements is set to about 1 mm which corresponds to 8.lambda.. Although this distance is very small, presence of physical warps on the magnetic recording medium interferes with the ability to issue highly precise output signals.
When such physical warps are present on the magnetic recording medium, the output signals from the magnetic resistor elements contain undulations of an opposite phase. Presence of such opposite phase undulations develops a level gap between the output signals. When these output signals are passed through a wave shape discriminating circuit and converted to a two value signal of H or L levels through comparison with a given threshold value for digital data processing, the two value signal includes pulses of different width, thereby causing detectoin errors.